1. Technical Field
The invention relates to a method driving a liquid crystal display device, and more particularly, to a method of inversion-driving a common electrode of a liquid crystal display device using an active matrix substrates.
2. Related Art
Recently, for a notebook type personal computer or a monitor, a liquid crystal display device employing an active matrix circuit using active elements such as a thin film transistor (TFT) has be rapidly popularized.
In a general liquid crystal display device using a nematic phase liquid crystal material, the liquid crystal material is controlled by a potential difference between a pixel electrode which is switched by active elements sandwiching the liquid crystal materials therebetween and a common electrode, and thus the display states of the pixels are controlled. When the potential difference between the pixel electrode and the common electrode is large, that is, at the time of black display in a normally white mode or at the time of white display in a normally black mode, a maximum potential difference between the common electrode and the pixel electrode is generally 3 V to 5 V, although it varies depending on the used liquid crystal material, a liquid crystal mode, and a liquid crystal gap. In the liquid crystal display device, in order to ensure reliability of the liquid crystal element, current drive for inverting the polarity of a voltage applied to the liquid crystal in a given time is required, and, if the potential of the common electrode is fixed, a potential signal written to the pixel electrode, that is, a potential amplitude of an image signal input to a data line of an active matrix circuit, becomes 6 V to 10 V.
When the image signal input to the data line is written by an external data driver IC, in order to output the potential amplitude of at least 5 V, an expensive IC manufactured by a high-breakdown-voltage process must be used instead of a general MOS process. Accordingly, the manufacturing cost increases and power consumption increases. Thus, a driving method of using a common inversion drive for inversion-driving a common electrode every polarity to reduce the amplitude of the signal input to a data line was suggested (See JP-A-62-49399).
In polarity inversion, there are a field inversion drive, a gate inversion drive, a source inversion drive, and a dot inversion drive. These drive methods are for setting the polarity of the common electrode of the pixels at any timing, and flicker becomes gradually less visible in the order of the field inversion drive, the gate inversion drive or the source inversion drive, and the dot inversion drive. Accordingly, in the gate inversion drive or the source inversion drive, and more particularly, the dot inversion drive, display quality is improved and it is difficult to generate flicker. Thus, it is possible to reduce a frame frequency and thus to easily realize low-power-consumption driving.
However, when common inversion drive is performed, since a constant relaxation time is required in common inversion, the polarity inversion can be performed in only one scanning period or one field period and thus it is impossible to perform the source inversion drive or the dot inversion drive. In order to solve the problem, in JP-A-11-142815, a method of patterning a common electrode and separately driving the common electrodes was suggested. However, since the common electrode is not patterned in general or is patterned using a patterning technology having low precision, in order to manufacture the common electrode in a shape suggested in JP-A-11-142815, an additional photolithographic process is required and thus the manufacturing cost thereof increases. Furthermore, in the display having high definition, the assembling precision of a pixel array and a color filter substrate is disadvantageous and thus it is difficult to realize this method. Moreover, in Japanese Patent No. 2982877, a method of alternately and symmetrically inverting the pixels with respect to the gate line so that the gate inversion drive appears to be the dot inversion drive was suggested. However, in this method, when displaying characters or straight line data, since the line on the same scanning line is displayed in a zigzag shape, display quality is deteriorated. In order to solve this problem, an IC for processing an external image signal is required and thus the manufacturing cost thereof increases.